[kamesama980]

bead-tearing: I've seen more sidewall damage running underinflated tires than overinflated. either way the tire won't fall apart from it unless the person doing the demounting screws it up. I worked in a tire shop the last 2.5 years. For liability reasons we couldn't inflate over the sidewall max and unless the customer specifically asked for it weren't supposed to go over the placard (tho I usually did a little) I've never had trouble going over the placard but under the sidewall.

inflations effect on economy: it will always increase straight line steady speed economy, it's just a matter of how much. after a while it's a diminishing-returns scenario. Truck tires at 110psi vs passenger tires at 35 psi...35 to 44 psi is almost 25%. the same increase in a 18-wheeler wouldn't be an extra 9 psi but an extra 28..almost 140 psi. Again, diminishing returns since the semi-tires are run higher to start with relatively speaking and are constructed for capacity and RR more than comfort and grip. they're factors, but far less so than passenger car tires.

Even among car tires and cars themselves, the amount of margin is going to be different for every tire and even sizes within tires. there's no one set amount that works for every car equally. My moms buick responds brilliantly to increased pressure, however my 1/4t pickups don't notice (measurably) anything over 30 psi. BUT it's almost 150% of the placardmy mom's buick is a 60/40 weight split 3800lb empty car with a placard rating of 30 psi, my truck weighs 2800lbs with 35 psi on the placard.
02 Lesabre @ 30 psi=30 mpg hwy doing under 65 mph empty or 1 passenger
02 Lesabre @ 44 psi=35 mpg @ 70 with 3 ppl and 300 lbs of luggage
I've seen cars with noticeable underinflation wear AT the placard pressure (early 2000s mitsu diamante IIRC at 28 psi front + rear) the placards are first and foremost for comfort, second for safety, third for FE.

I would bet placard pressures come up a lot in the next few years. CAFE is supposed to be up to 35 mpg by 2018 (with increments before then) which is putting a lot of pressure (no pun intended) on the manufacturers.

In Summary: yes you can go over the sidewall ratings, but it's your a$$ on the line, the numbers are to keep their liability down. I recommend somewhere between the placard and the sidewall, leaning on the higher side.